Apparatus for cleaning gas swept heating surfaces



B. O. BROMAN Jan. 5, 1954 APPARATUS FOR CLEANING GAS SWEPT HEATINGSURFACES 2 Sheets-Sheefll Filed June 2, 1949 INVENTOR 5.0.5/PaM/7/ATToRNEYs Jan. 5, 1954 B. o. BROMAN 2,565,118

APPARATUS FOR CLEANING GAS SWEPT HEATING SURFACES Filed June 22, 1949 2Sheets-Sheet 2 INVENTORY 5. 0. aka/v27,

W MVM ATTORNEYS Patented Jan. 5, 1954 APPARATUS FOR CLEANING GAS SWEPT-HEATING SURFACES Bror 010i Broman, Stora Essingen, 'Sweden, "assignorto Aktiebolaget A.-Ekstroms Maskinaffar,

Stockholm, Sweden Application June 22, 1949, Serial No. 100,645

Claims priority, application Sweden January 19, 1949 11 Claims.

This invention relates to a methodand an apparatus for cleaning, duringoperation, heating surfaces swept by air or gas by using sand, finegravel, granulated metal particles (particularly steel shot) or similarsolidparticles which are caused to drop by gravity on the heatingsurfaces, their falling speed in some cases being increased on accountof the velocity of the gas along the surfaces, the particles, however,never being directly blown against the heating surfaces by the action ofcompressed air or the like.

Tests have established that in order to obtain the highest practicaleffect, the cleaning operation in accordancewith this invention must becontinuous. For this purpose a fixed portion of solid particles (forexample steel pellets) which may be relatively small, is, by means ofsuitable arrangements, causedto circulate throughthe apparatus to becleaned. The steel pellets or particles may also be cleaned during thecirculation, possibly by washing, be dried and :even cooled in order tosave the transportdevices.

For cleaning gas-swept heating surfaces for instance in boilers andeconomizers during operation blowing with steam or air iswidely used.

In certain cases, especially for economizers and air pre-heaters heatedwith combustion gases from soda furnaces in cellulose plants the heatingsurfaces are cleaned during operation by means of water or some alkalinesolution sprinkled or flushed thereon.

The above-mentioned cleaning methods suffer from serious disadvantages.

When blowing with steam or air, the costof the requisite apparatus isrelatively high, and the costs for steam'and compressed air are alsoquite considerable.

The sprinkling with water or some alkaline solution entails risks to theheatingsurfaces on account of the resulting considerabletemperaturestresses which in many cases cause considerable damage to theconstructions in a relatively short time.

When cleaning is effected by means of water, air or steam, it isnecessary as a minimum to effect a cleaning operation once every eighthhour i. e. three'times during each period of 24 hours in continuousoperation of the plant.

It has further been suggested to employ sandblasting, i. e. injectingsolid particles with .the aid of compressed air. However, in practicethis method has not proved acceptable as the heating surfaces becomedamaged by the sandblasting.

The general object of this invention is therefore to provide a method ofcleaning gas-swept 2 heating surfaces of-a heat plant during operationat lowcosts and'without any risks-of damagingthe heating surfaces or anyother parts of the plant by using solid cleaning particles which arecirculated through the plant andare caused to drop against the surfacesto be cleaned.

' A further object of the invention is to provide apparatus by which thecleaning particles are circulated through the plant and caused to fallagainst the surfaces to be cleaned.

A still further object of the invention is to provide distributing meansfor spreading the cleaning particles over the surfaces to becleaned in apredetermined manner prior to their falling steel pellets and Figs. 6and 7 show corresponding views of another embodiment of suchdistributor.

As regards the drawing, Figure l discloses the invention with referenceto heat interchanging apparatus that are associated with the boilerplant. The apparatus includes a casing l embodying side walls and atop-wall. An upper gas inlet l communicates with the casing through aside wall thereof at an area adjacent the top wall-and a lower gasoutlet 1 communicates with the casing adjacent the lower extremitythereof. Within the casing are arranged tube means through which fluidpasses for heat exchanging relationship with the gas that flows throughthe casing. The tube means include a preheater 2 for preheating primarycombustion air, an economizer 3 consisting of spaced banks of tubesextending through the casing a horizontal relationship and a preheater 4for secondary combustion air. These respective tube means are mountedvertically above one another. Above the casing is a container 5. Thiscontainer at its lower endcommunicates through cated generally at 1 issecured to the bottom end of the hollow shaft and, as apparent fromFigures 4 to 6, this rotary distributing member has an outer contour ofspiral form that extends from the vicinity of the center rotationthereof outward toward and terminates at its greatest radius. Anelectric motor 8 and suitable gear means rotates the hollow shaft thatsupports the rotary distributing member "I so that solid cleaningparticles, for instance shot pellets, are effectively distributed withinthe casing above the tubes and spread throughout substantially thecross-sectional area of the casing so that they fall by gravity andcascade through the casing to impact and ricochet against the surfacesof the tubes to pick up material accumulated thereon and to dislodgematerial therefrom so as to clean the tubes. Beneath the casing and thusbeneath the gas outlet are means for collecting the cleaning particleswhich includes a conduit 9 constituted by a return pipe connected to thecontainer at one end and its other end is in communication with a fanIt] that blows air through the conduit or pipe 9 for returning theparticles to the container 5 so that continuous circulation can bemaintained.

In the embodiment according to Fig. 2 a screw conveyor Ii and a bucketcarrier l2 are substituted for the return pipe, but otherwise theapparatus is analogous to and operates in the same manner as the oneaccording to Fig. 1. In the apparatus according to Fig. 3, the path ofthe gas from a boiler I3 through the apparatus is indicated by arrows,and the velocity of the flowing gas will contribute to the accelerationof the speed of the cleaning particles.

Figs. 4 and 5 show an embodiment of a distributor member. The numeral il designates the hollow shaft for feeding the cleaning particles, towhich a plate 'I is secured, the contour of which follows a spiral line,said plate being provided with radial ridges l5. The purpose of thisdevice is to bring about an even distribution of the cleaning particlesover the cross section of the apparatus located underneath. On theplate, directly under shaft [4 a wear resistant plate I6 is arranged,having sloping sides in order to prevent the cleaning particles fromcollecting in a heap below the shaft; instead it is immediately shovedout to the periphery of the plate.

The plate 16 is made of particularly wear-resistant material to insurelong life of the distributor member. The plate forming the base ofdistributing member 1 extends transverse to the axis of the shaft l4 andis in spaced relation with respect to the lower end of this shaft. Thevanes l5 that extend radially of the hollow shaft from the shaft towardand terminate at the outer marginal edges of the plate are substantiallyequispaced and of unequal length as shown in Figure 5.

Another distributing member for the same purpose is shown in Figs. 6 and7 and consists mainly of two more or less conically shaped plates I! andI8, arranged above each other and held together by radial walls andstays. The plates have a spiral-like, outside contour and the upperplate ll is provided with an inlet 19, eccentrically fastened to thepipe [4. The eccentricity being adjustable, the desired distributioncharacteristics of the steel particles is attained in operation. Rightbelow the inlet I9 is disposed a plate 20, having sloping sides and madeof wear-resistant material to minimize the effect of wear and tearcaused by the particles.

In the arrangement of Figures 6 and 7, the distributing member, asindicated, includes a collar constituting the inlet I9 and the conicallyshaped plates I1 and [8 each have the aforedescribed spiral contour andthe plate 18 is smaller than the plate ll. Radial vanes l5 arrangedsimilarly to the vanes [5 of Figures 4 and 5 extend between the platesfrom the outer edges thereof toward and terminate adjacent the collar.The uppermost plate has an aperture therein at its apex and the insert20 of wear resistant material is mounted in an aperture in the lowermostplate that is in alignment with the aperture in the uppermost plate.

In order to limit the free fall of the particles, groups of spaced rodsI extend between the walls of the casing above the tubes to be cleanedbut in spaced relation beneath the distributing member.

It is therefore clear that the solid cleaning particles are continuouslyfed to the distributing member and effectively distributed throughoutthe entire cross-sectional area of the casing so that they falldownwardly therethrough in the same direction as the gas flow strikingthe outer surface of horizontally arranged tubes and passing between thetubes of nests of tubes and thus internally of the vertically arrangedtubes of the preheater 2.

The cleaning particles may be introduced by means of a low-speed airblow or blast, but no real sand-blowing effect may be directed towardsthe heating surfaces proper.

The method according to the present invention has proved most valuableespecially when the gases carry a large percentage of solid matter, orwhen said matter is of a sticky nature, causing injurious coatings onthe heat surfaces, or when the gases contain substances which chemicallyattack these surfaces. Besides, the apparatus according to thisinvention is less expensive, both as to cost and operation, than themethods and apparatus heretofore used for the purpose.

From practical tests according to the invention, when using steelpellets, it has been established that the height of free drop of thesolid particles should preferably not be too long. For this purpose, forinstance, one or more sets of rods may be arranged, preferably above thetopmost set of tubes in the boiler, to prevent the pellets from fallingdirectly on the tubes. For different tubes, the height of free fall forthe particles of pellets has different maximum values. In some cases itshould not be more than 250 mm. above the topmost group of tubes tobreak the fall. The size, shape and weight of the particles also haveinfluence upon the cleaning effect, imparted to the heating surfaces.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In heat interchanging apparatus, a casing including side walls and ato wall, an upper gas inlet communicating with the casing through a sidewall thereof adjacent the top wall and a lower gas outlet communicatingwith a side wall of the casing, tube means within said casing andthrough which fluid passes for heat exchanging relationship with gasflowing through the casing, a rotatable hollow shaft projecting throughthe top of the casing and terminating above the tube means therewithin,a rotary distributing member secured to said hollow shaft and saidmember having an outer contour of spiral form extending from thevicinity of the center of rotation thereof outward toward andterminating at its greatest radius, means for feeding solid cleaningparticles into the hollow shaft so that said particles are distributedwithin the casing above the tubes and spread throughout substantiallythe crosssectional area of the casing to fall by gravity and cascadethrough the casing and impact and ricochet against the surfaces of thetubes to pick up material accumulated thereon and to dislodge materialtherefrom to clean the tubes, and means beneath the casing and beneaththe gas outlet to collect said cleaning particles after they have passedthrough the casing.

2. In heat interchanging apparatus as defined in and by claim 1, inwhich said rotary distributing member is eccentrically and adjusta-blysecured to said hollow shaft.

3. In heat interchanging apparatus as defined in and by claim 1, inwhich said rotary distributing member is fixedly secured to said hollowshaft comprises a plate extending transversely of the axis of the shaftand in spaced relation with respect to the terminal end of the shaft,said plate having the said outer contour of spiral form extending fromthe vicinity of the center of rotation of the shaft outward toward andterminating at its greatest radius, and vanes mounted on said plate andextending radially of said hollow shaft from the shaft to andterminating at the outer marginal edge of the plate, said vanes beingsubstantially equi-spaced and of unequal length.

4. In heat interchanging apparatus as defined in and by claim 3, inwhich said plate is of wear resistant material to minimize wearoccasioned by the movement of the cleaning particles relative to theplate.

5. In heat interchanging apparatus as defined in and by claim 1, inwhich said rotary distributing member includes a collar, verticallyspaced plate members carried by the collar and having said spiral outercontour, said plate members further having conical shape incross-section and the lowermost plate being smaller than the uppermostplate, radial vanes extending between the plates from the outer edgesthereof toward and terminating adjacent the collar, said uppermost platehaving an aperture therein at the apex thereof surrounding said collar.

6. In heat interchanging apparatus as defined in and by claim 5, inwhich the lowermost plate has an aperture therein at the apex thereofand an insert of wear resistant material disposed in said aperture tominimize wear occasioned by movement of said particles relative to saidplate.

7. In heat interchanging apparatus as defined in and by claim 1, andfurther including particle receiving means disposed above said casingand conveying means extending between the collecting means and saidparticle receiving means to convey particles from the collecting meansto the receiving means and conduit means connecting said receiving meanswith the said feeding means.

8. In heat interchanging apparatus as defined in and by claim 1, andgroups of spaced rods supported within the walls above the tubes andspacedly beneath said distributing member to limit the height of freefall of the cleaning particles.

9/Means for cleaning gas-swept heating surfaces of heat interchangingapparatus, which apparatus is of the type embodying walls defining acasing and means providing heat exchange surfaces within the casing andgas inlet and outlet means communicating with the casing, comprising arotary distributing member disposable within the casing directly abovethe surfaces to be cleaned, said member having an outer contour ofspiral form extending from the vicinity of the center of rotationthereof outward toward and terminating at its greatest radius, and meansfor feeding solid cleaning particles to said distributing member so thatthe particles are simultaneously introduced within and spread throughoutsubstantially the cross-sectional area of the cas ing directly above thesurfaces to be cleaned.

10. A rotary distributing means for simultaneously introducing anddistributing solid cleaning particles within the walls of a casing of aheat interchanging apparatus and above the heat exchange surfaces withinthe casing that are to be cleaned, comprising a hollow rotatable shaftand 1 cans providing rotary distributing surfaces extending transverselyof the axis of the shaft and having an outer contour of spiral formextending from the vicinity of the center of rotation of the shaftoutward toward and terminating at the greatest radius of said member,spaced radial vanes extending inwardly from the outer edge of saidtransversely extending means toward said shaft, and means securing saidtransversely extending means to said hollow shaft.

'11. A rotary distributing means as defined in and by claim 10, in whichsaid last mentioned means adjustably eccentrically secure saidtransversely extending means to said hollow shaft,

BROR OLOF BROMAN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,613,638 Altimari et a1 Jan. 11, 1927 1,795,348 Schmidt Mar.10, 1931 1,916,337 Schmidt July 4, 1933 2,379,195 Simpson et al June 26,1945 2,468,712 Kohler Apr. 26, 1949 FOREIGN PATENTS Number Country Date587,774 Great Britain May 6, 1947

